Obesity and diabetes including type 2 diabetes are representative metabolic diseases that occur in modern society. These diseases are regarded as health-threatening factors in the world and the accompanying economic costs due to the incidence of these diseases are rapidly increasing at present.
Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are representative gastrointestinal hormones and neuronal hormones and are materials involved in the control of blood glucose levels according to food intake. Glucagon is a peptide hormone secreted by the pancreas and is involved in controlling the blood glucose levels along with the two materials described above.
GLP-1 is a hormone secreted by the small intestine stimulated by food intake. GLP-1 promotes insulin secretion in the pancreas in a blood glucose-dependent manner and inhibits the secretion of glucagon, thus helping the action of lowering blood glucose levels. Additionally, GLP-1 has the roles of slowing digestive action in the gastrointestinal tract by acting as a satiety factor, and reducing the amount of food intake by delaying the time for emptying digested food in the gastrointestinal tract. Furthermore, the administration of GLP-1 to rats was reported to have effects of inhibiting food intake and reducing body weight, and these effects were confirmed to occur equally both in normal and obese states, thus showing the potential of GLP-1 as an agent for treating obesity.
GIP, one of the gastrointestinal hormones secreted by the stimulation of food intake as is the case of GLP-1, is a hormone consisting of 42 amino acids secreted by the intestinal K-cells. GIP was reported to perform the functions of promoting the secretion of insulin in the pancreas in a blood glucose-dependent manner and helping to lower the blood glucose levels, thereby exhibiting the effects of increasing the activation of GLP-1, anti-inflammation, etc.
Glucagon is produced in the pancreas when the blood glucose levels fall due to reasons such as medications, diseases, deficiency in hormones or enzymes, etc. Glucagon sends a signal for glycogen breakdown in the liver to induce the release of glucose and increases blood glucose levels to a normal level. In addition to the effect of increasing the blood glucose levels, glucagon suppresses appetite in animals and humans and activates hormone-sensitive lipase of adipocytes to promote lipolysis and energy expenditure, thereby showing an anti-obesity effect.
As such, active studies are being conducted to develop GLP-1 as a therapeutic agent for treating diabetes and obesity, based on the effects of GLP-1 controlling blood glucose levels and reducing body weight. Currently, exendin-4, prepared from lizard venom and having an amino acid homology of about 50% with GLP-1, is under development as a therapeutic agent for treating the same kinds of diseases. However, the therapeutic agents containing GLP-1 and exendin-4 were reported to show side-effects such as vomiting and nausea (Syed Y Y., Drugs, 2015 July; 75 (10): 1141-52).
Additionally, for the maximization of body weight reduction and as an alternative to the above-described GLP-1-based therapeutic material, studies have been focused on dual agonists having activities to both GLP-1 receptors and glucagon receptors, and they were shown to be more effective in body weight reduction due to the activation of glucagon receptors, compared to when the existing GLP-1 was treated alone (Jonathan W et al., Nat Chem Bio., 2009 October (5); 749-757).
Additionally, in the study related to triple agonists, which have activities to all of GLP-1, GIP, and glucagon receptors simultaneously, efforts have been made recently to increase the half-life of the triple agonists by substituting an amino acid sequence to increase the resistance to dipeptidyl peptidase-IV (DPP-IV), which decomposes gastrointestinal hormones to get rid of their activities, followed by adding an acyl group to a particular region thereof (Finan B et al., Nat Med., 2015 January; 21 (1): 27-36). However, their effects of activating three different kinds of receptors were not significant and no triple agonist showed various active ratios thereto.
Accordingly, there is a need for the development of a novel material which can highly activate GLP-1, GIP, and glucagon receptors and has the effects of controlling blood glucose levels and reducing body weight without causing any side-effects such as vomiting and nausea.
Additionally, there is also a need for the development of a novel material which has various active ratios to GLP-1, GIP, and glucagon receptors. For example, there is an increasing need for the development of a material which has an effect of reducing body weight but has a significantly higher effect of controlling blood glucose levels due to high GLP-1 and GIP activities but with relatively low glucagon activity for a hypoglycemic effect; or a material which has high activities for all of GLP-1, GIP, and glucagon, thus having a significantly high effect of reducing body weight.
Additionally, GLP-1, GIP, and glucagon have low in vivo stability and thus they have a disadvantage in that they must be administered daily or twice daily when they are applied to humans for therapeutic uses.